The set of real numbers symbol is the Latin capital letter “R” presented with a double struck typeface. The symbol is typically used to express that a variable is a member of the set of real numbers:
In plain language, the expression above means that the variable is a member of the set of real numbers.
Symbol  Format  Data 

ℝ  Unicode 

TeX 


SVG 
The set of real numbers contains the set of rational numbers as well as irrational numbers like pi, e, and the square root of two.